Circuit interrupter



Feb. 19,1935. B. P. BAKER Em 1,99 ,818

CIRCUIT INTERRUPTER Filed Jan. 24, 1951 2 Sheets-Sheet 1 34 INVENTOR 5:

Berybm/h PBaA er' andMr'vfiirop M Leeds.

ATT'ORNEY Patented Feb. 19, 1935 PATENT OFFICE CIRCUIT INTERRUPTERBenjamin P. Baker, Turtle Creek, and Winthrop M. Leeds, Wilkinsburg,Pa., assignors to Westinghouse Electric and Manufacturing Company, acorporation of Pennsylvania Application January 24, 1931, Serial No.510.990

30 Claims.

Our invention relates to circuit interrupters and particularly tocircuit interrupters of the liquid-immersed type.

One object of our invention is to provide a circuit interrupter of theabove-mentioned type with a magnetic chamber which confines the arc andinfluences its movement within the chamber.

Another object of our invention is to provide a magnetic pot-typestructure for a circuit interrupter of the above-mentioned type thatshall have a plurality of slotted insulating members mounted within itin such manner that the slots of the members are aligned with the arcpath.

A further object of our invention is to provide a chamber of magneticmaterial with a slot in its side wall which is aligned with slots ofinsulating plates mounted within the chamber for the purpose ofeffecting a predetermined .arc movement within slots f the insulatedplates.

A still further object of our invention is to provide recesses along thesides of the slots of the insulating members of the above-describedstructure that shall retain a portion of the fluid in which thestructure is immersed, adjacent to the arc, as the arc is moved in theslots.

A still further object of our invention is to provide an enclosingchamber for a plurality of slotted plates of the above-mentioned typethat shall be provided with a plurality of vents in the side wallthereof that conform with the slots in the plates.

A still further object of our invention is to provide a chamber of theabove-mentioned type, having a plurality of slotted plates mountedtherein, with vents at the top side portion thereof conforming with. theslots in the plates and with a substantially closed bottom'portion toeffect upward movement of the gases evolved by the arc.

Our invention will best be understood by referring to the followingspecification, taken in conjunction with the accompanying drawings,wherein:

Figure l is a sectional view, in elevation, of a circuit interrupterembodying my invention.

Fig. 2 is an enlarged sectional view. in elevation, of a portion of thearc-extinguishing structure shown in Fig.1 and taken along the lineII-II of Fig. 3, thereof, and illustrates one embodiment of myarc-extinguishing structure.

Fig. 3 is a sectional view of the arc-extinguishing structure shown inFig. 2, taken along the line III-III thereof.

Figs. 4 and 5 are plan views of unit members employed in the structureshown in Figs. 2 and 3.

Fig. 6 is a sectional view, in elevation, of a modified form of thearc-extinguishingstructure illustrated in Figs. 1 to 5, inclusive.

Fig. 7 is a sectional view of the structure shown in Fig. 6, taken alongthe line VII-VII thereof.

Fig. 8 is a side-view, in elevation, of the structure shown in Fig. 6.

Fig. 9 is a plan view of a unit member employed, along with the unitmembers shown in Figs. 4 and 5, to constitute the plate structure shownin Figs. 6 and 7. v

Fig. 10 is a sectional view. in elevation, of a modified form of thearc-extinguishing structure shown in Figs. 2 and 6.

Fig. 11 is a side view of the structure shown in Fig. 10.

Fig. 12 is a sectional view, taken along the line 1HI-XII of Fig. 14 ofa further modified form of our arc-extinguishing structure shown inFigs. 2, Band 11. I

Fig. 13 is a side view, in elevation, of the structure shown in Fig. 10.

Fig. 14 is a sectional view of the structure shown in Figs. 12 and 13,taken along the line XIVX'[V of Fig. 12.

Fig. 15 is a plan view of a'unit member employed in the structure shownin Figs. 12, 13 and 14.

Our invention comprises, in general, a casing 1 having a cover 2supported thereon by bolts 3. The cover 2 supports the insulatedconductors 4 by means ofthe flanges 5 and bolts 6, in a well knownmanner. Arc-deionizing-and-extinguishing devices 7 are supported on theenclosed ends of the conductors 4 and are provided with stationarycontact members 8 which are bridged by a conducting bar 9. Theconducting bar 9 is supported and actuated by means of the lift rod 11which extends through the cover 2. A suitablearc-quenching liquid 12 iscontained within the casing 1 in which the contact-members 8,theconducting bar 9 and, the arc-extinguishing dequenching fluid istrapped ahead of the arc. As the arc is moved toward the rear of theslot, the oil, retained in the pockets, is decomposed by the arc, andthe gas is forced'transversely throughv the arc stream to cause the arcstream to be deionized by the turbulent flow of the gas therethroughuntil, upon the occurrence of a current zero in the course of itsalternating cycle, the arc is extinguished. After the arc isextinguished,

the presence of the un-ionized gas in the space between the terminalsquickly disintegrates the ionized stream therebetween so that theimpressed voltage across the terminals is incapable of risingto suchvalue as to cause arc reinitiation between the terminals.

In the present invention, similar plates having slots and recesses fortrapping the oil adjacent to thearc path are employed, and the platesare enclosed within a chamber which is constructed of magnetic materialthat is employed to control the movement of the arc and the arc gaswithin the chamber. In order to effect a turbulent flow or un-ionizedgas within the arc stream, our present structure effects a horizontaland a vertical flow of the gas within the slotted structure.

The arc-extinguishing device 7, shown enlarged in Fig. 2, comprises amagnetic casing 13 forming an inner shell surrounded by an outer shellof insulating material 14 and having groups of plates 15 distributedhorizontally within the casing.

Two groups of insulating plates are provided within the casing 13, agroup 17 comprising three plates 18 of fiber having a central hole 19and a communicating slot 20, as shown in Fig. 4. A second group ofplates 21 comprises three plates 22, as shown in Fig. 5, that are madeof insulating material, such, tor example, as fullerboard, which absorbsthe arc-quenching liquid. A central hole 19 is provided in the plates,together with holes 23 which communicate with the central hole 19 bymeans of the slots 24. When the groups of plates 22 are assembledbetween groups of plates 18, the holes 23 constitute pockets or recessesin which the arc-quenching liquid is trapped and retained ahead of thearc, as the arc is moved in the slot.

The oil or like arc-quenching medium evolves an un-ionized gas in thepresence of an arc, and, in case suflicient of the liquid is not trappedin the pockets 23, the portion absorbed by the fullerboard material ofthe plates 22 will be available for liberating the gas. The fibrematerial of the plates 18, in the presence of an arc, also liberates anun-ionized gas. It will, therefore, be seen that, even in the absence ofthe liquid, our present construction will be almost as eflective forliberating un-ionized gas as when a quantity of decomposable liquid isactually trapped in the recesses.

As mentioned hereinabove, the trapped liquid in the recess 23 isretained ahead of the arc, as it is moved into the slot. Since ourconstruction effects a vertical flow of the evolved gas upwardly withinthe slot and recesses toward the vents at the top of the structure, aturbulent motion of the gas and the liquid ensues. The gas and theliquid are thus carried into the arc stream, as the arc is moved in theslots, where the un-ionized gas effects deionization of the arc path,and the particles of liquid are decomposed into a gas that furtherdeionizes the arc stream.

In order to provide a force to effect arc movement in the slots, themagnetic casing 13 is split longitudinally on its side opposite to thattoward which the arc is to be moved, as shown at 25.

meters Au insulating member 26 inserted in the open ing between the endsof the magnetic casing to'add. strengtl'i to the surrounding insulatingstructure 14. The open. magnetic casing which. comprises a magnet ofU-shape efiects a distorted magnetic field about the arc, and its movement away from the slotted side ensues.

A movable contact member 2'7 mountedon the conducting bar. 9, extendswithin an opening 28 in. the bottom of the chamber 13 having a tightsliding fit therewith in order to effect a seal to prevent anysubstantial flow of gas therefrom. A stationary contact member 29 isprovided on the top of the chamber 13 which is the means by which thechamber is secured to the contact 8 and to the conducting bushing 4.

Openings 30 are provided about the contact member 29 through which thegases generated within the chamber are vented. In this construction, thearc stream is subjected to a transverse flow of gas as the arc is movedwithin the slot and also to a vertical flow of gas as the gas movesupwardly to be vented from the opening 30.

The lateral arc movement in the slots is caused by the distortedmagnetic field above referred to, eflected by the split magnetic casing13 which surrounds the arc stream. Such a construction eliminates theiron plates heretofore distributed between the insulating plates foreffecting arc movement, as specified in the above-mentioned patent.

Referring to Figs. 6 to 9, inclusive, a modified form of ourarc-extinguishing structure is illustrated. In this construction, a gridstructure is built up by employing a plurality of insulating plates 18similar to those heretofore referred to and illustrated in Fig. 4. Theplates are alternately spaced by iron plates 31, shown by the brokenline in Fig. 7, and insulating plates 22' shown in Fig. 9 that aresimilar to plates 22 shown in Fig. 5, with the exception of theprovision of a vent 32.

The plates are assembled within an insulating casing 33 which has aseries of openings 34 to register with the vents 32 of the plates 22'.The upper portion of the chamber 33 is provided with a stationarycontact member 35. A movable contact member 27 fits snugly in theopening 28 in the bottom of the chamber 33 through which it extends toengage the stationary contact member 35.

In this construction, when an .arc is established between the contactmembers 27 and 35, the presence of the magnetic plates 31 causes the arcto be moved laterally in the slots. The liquid 12, trapped within thepockets 23 of the plates 22 is decomposed, and the resulting gas passestransversely through the arc stream. The gas, upon passing through thearc, becomes heated and ionized and is thereafter cooled and deionizedduring its passage through the slots 32, while in intimate contact withthe cool surfaces of the adjacent insulating plates 18.

Figs. 10 and 11 disclose an embodiment of our invention that is similarto the one described above, as shown in Figs. 6 and 8, with theexception that unvented plates 22 are used in the lower portion of thestack, and the slots 32 are provided in plates 22' only in the upperportion of the structure.

In this construction, the decomposed gases not only pass transverselythrough the arc stream but also pass vertically therethrough, as theymove upwardly within the slots to pass from the this application.

vents 34. In each of the modifications, it is our desire to pass as muchof the cool un-ionized gas through the arc stream as is possible, andthe constructions heretofore described effect this large turbulent flowby having the gas pass both horizontally and vertically through the arcstream.

Referring to Figs. 12 and 15, inclusive, in which a modification of thestructure shown in Figs. 2 and 3 is shown, the arc movement is effectedby the employment of the enclosing casing 13 constructed of magneticmaterial that is provided with an opening at one of its sides. Inthisconstruction,'a contact-bar 37 extends within the slot 38 and, whenmoved to closed-circuit position, engages the stationary contact member39.

Plates 22' similar to those disclosed in Fig. 9, are employed to providepockets for the arcextinguishing liquid, while plates 41, locatedtherebetween, are provided with a long narrow slot 42. When an arc isdrawn, upon the movement of the conducting bar 37 downwardly away fromthe stationary contact member 39, the infiuence of the magnetic casing13 causes the arc to be moved laterally within the slots 42 away fromthe opening 43 provided in the side of the chamber 36. During thismovement, the gas passes turbulently through the arc stream and,

as explained hereinabove; upon extinguishment;

the arc will be prevented from reigniting.

It will thus be seen that we have provided a deionizing andarc-extinguishing device that utilizes means for moving the are intopockets of arc-quenching liquid and for causing the gases, evolved fromthe liquid in the presence of the arc, to pass turbulently through thearc stream. The movement of the arc is effected by the presence ofmagnetic material about the arc path which may be either platesinterposed between insulating plates or may be the material employed inthe enclosing casing that provides a distored magnetic field about thearc path because of a cutaway portion on one of its sides. The turbulentfiow of gas throughout the arc path is eifected by a construction whichcauses the gas to fiow transversely through the arc stream and byventing the slots at one of its ends to cause the gas to also fiowverticallytherethrough.

While we described several embodiments of our invention, it is to beunderstood by those skilled in the art that many modifications,additions, omissions, andsubstitutions may be made thereinwithoutdeparting from the spirit and scope of our invetnion, as set forth inthe accompanying claims.

Application, Serial No. 599,678 of W. M. Leeds, filed March 18, 1932, isa continuation in part of We claim as our invention:

1. A chamber associated withthe contact members of a circuit interrupterprovided with venting means in the wall thereof, and a plurality ofplates within the chamber some of which are provided with slots whichare aligned with the venting means in said chamber.

2. A chamber associated with the contact members of acircuit interrupterprovided with venting means in the wall thereof, and a plurality ofplates within the chamber some of which are provided with slots whichare aligned with the venting means in said chamber and recesses in theplates associated with the slots.

3. An arc extinguishing chamber for association with the contact membersof a circuit-interrupter, said are extinguishing chamber having an outershell provided with venting means the sidewall thereof, and a pluralityof plates within the chamber some 01'- which are provided with slotswhich are aligned with the venting means in said shell and recesses inthe plates associated with the slots and magnetic. means.

for eflecting arc movement toward said recesses.

4. An arc extinguishing chamber for associa-- tion with the contactmembers of a circuit interrupter, said are extinguishing chamber havingan outer shell provided with venting means along one side at the topportion thereof only and a plurality of slotted plates within saidchamber with the ends of said slots leading to said venting means.

5. A chamber associated with the contact members of a circuitinterrupter and provided with venting means in the top portion thereof,a plurality of plates positioned within said chamber and havingelongated slots extending toward said venting means and a contact:member extending;

structure including means of insulating material having an openingtherethrough having narrow portions, means for causing an arc in saidopening in said are extinguishing structure, an enclosing casingsurrounding said are extinguishing structure, said enclosing casingincluding a member of magnetic material which is generally cylindricaland of such configuration as to move the arc in said opening in the arcextinguishing structure due .to the reaction between the arccurrent andthe magnetic material of the enclosing casing.

8. In a circuit interrupter, an arc extinguishing structure including aplurality of plates of insulating material having elongated slotstherein, said slots being aligned forming a groove, means for causing anarc in said are extinguish ing structure, an enclosing casingsurrounding said are extinguishing structure, said enclosing casingincluding a member of magnetic material which is generally cylindricaland of such configuration as to move the arc in said aligned slots inthe insulating plates of the arc extinguishing structure due to thereaction between the arc current and the magnetic material of theenclosing casing.

9. In an arc extihguishing structure for a circuit interrupter, acylindrically shaped enclosing casing of magnetic material having a slotin one side extending longitudinally thereof, said enclosing casing. ofmagnetic material distorting the magnetic field due to the arc currentto move the arc, and forming a-pressure chamber about the arc.

10. In an arc extinguishing structure for a circuit interrupter,anenclosing casing forming a pressure chamber and including an outershell of insulating material and an inner shell of magnetic materialhaving a slot extending longitudinally along one side thereof, andinsulating means in said casing defining a narrow groove extendingsubstantially the length of said casing.

11. In a circuit interrupter, a body of liquid, an arc extinguishingstructure including means oi insulating material having a passagetherethrough, means for causing an arc in said passage, and said meansof insulating material having portions extending into close proximity tothe path where the arc is caused and having recesses opening into saidpath for retaining said liquid, a generally cylindrical casing enclosingsaid means of insulating material, and venting means extending throughthe side wall of said cylindrical casing on one side only from anyportion along the length of said passage.

12. In a circuit interrupter, a movable contact member and an arcextinguishing structure including a stack of plates having openingstherein through which said contact member is movable, said openings insome of said plates having portions of a width not materially greaterthan the width of said movable contact member, and said openings in someof said plates extending to one outer edge thereof, a cylindrical casingenclosing said stack of plates, and venting means in the side wall ofsaid casing aligned with said openings which extend to the edge of someof said plates.

13. In a circuit interrupter, a body of liquid, a movable contactmember, and an arc extinguishing structure including a stack of plateshaving openings therein through which said contact member is movable,said openings in some of said plates having a closed periphery andhaving portions of a width not materially greater than the width of.said movable contact member, and said openings in other of said platesforming pockets for retaining said liquid and extending to one outeredge of the plates, a cylindrical casing enclosing said stack of plates,and venting means in the side wall of said casing aligned with saidopenings which extend to the edge of some of said plates.

14. In a circuit interrupter, a relatively fixed contact member and amovable contact member, a body of liquid, and an arc extinguishingstructure including a stack. of plates of insulating material havingopenings therein through which said movable contact member is actuated,said openings in some of said plates at intervals along the length ofthe stack having a closed periphery and having portions of a width notmaterially greater than the width oi. said movable contact member, saidopenings in some of said plates at intervals along the end of said stackadjacent said fixed contact forming pockets for retaining said liquidand extending to an outer edge of the plates, and said openings in someoi said plates at intervals along the other end of said stack formingpockets for retaining said liquid, and a cylindrical casing enclosingsaid stack of plates and having venting means in the side wall thereofopposite and aligned with said openings which extend to the edge of saidplates at the end of said stack adjacent said fixed contact only.

15. In a circuit interrupter, an arc extinguishing structure includingmeans of insulating material having a passage therethrough for the are,and an enclosing casing for said means or insulating material includinga generally cylindrical member of magnetic material having a slot alongone side thereof, and venting means in the wall of said enclosingcasing, said venting means having an area which is. small compared tothe longitudinal cross-sectional area of said enclosing casing wherebypressure is built up'in said enclosing casing and a blast of gas iscaused to flow out said venting means.

16. In a circuit interrupter, an are extinguishing structure includingmeans 01 insulating material having a passage therethrough for the arc,and an enclosing casing for said means of insulating material includinga generally cylindrical member of magnetic material having a slot alongone side thereof, and venting means in the side wall of said enclosingcasing through said slot, the width of said venting means being greatlyless than the internal width of said enclosing casing.

17. In a circuit interrupter, a body of liquid, an arc extinguishingstructure including a stack of plates having openings therethrough,means for causing an arc in said openings, some of said plates havingportions extending into close proximity to said are, and some of saidplates providing pockets for retaining said liquid adjacent to the arc,a casing enclosing said stack of plates and including a generallycylindrical member of magnetic material having a longitudinal slottherein, and venting means from said chamber having an area which issmall compared with the longitudinal cross-sectional area of saidenclosing casing for restricting the flow of gas therefrom. i

18. In a circuit interrupter, a movable contact member and an arcextinguishing structure including a stack of plates having openingstherein through which said contact member is movable, saidopenings insome of said plates having portions of a width not materially greaterthan the width of said movable contact member, and said openings in someof said plates extending to one outer edge thereof, a casing enclosingsaid stack of plates and including a generally cylindrical member ofmagnetic material having a longitudinal slot along one side thereof, andportions of said slot being open adjacent the openings in some of saidplates in which the openings extend to one outer edge thereof.

19. In a circuit interrupter, a movable contact member, and an arcextinguishing structure including a stack of plates of insulatingmaterial having openings therein through which said contact member ismovable, some of said plates of insulating material having portionsextending into close proximity to the path of said movable contactmember, and some 01 said plates of insulating material having saidopenings extending to one outer edge of the plates, a plurality ofplates of magnetic material positioned at intervals between said platesof insulating material, said plates of magnetic material having slotstherein extending to one outer edge thereof, and a generally cylindricalcasing enclosing said plates of insulating and magnetic materials, andsaid casing having openings in the side wall thereof aligned with someof said openings in said plates of insulating material in which theopenings extend to one outer edge of the plates.

20. An electric circuit breaker comprising in combination, a'containerfor oil, a switch structure supported within said container and at leastpartly immersed in and filled with said oil and including a cylindricalcasing having an internal switch chamber, relatively movable electrodesmounted in said switch chamber and also immersed in said oil and aplurality, of transverse bailie platessecured in said cylindrical casingand dividing said switch chamber into a plurality of shallow chambers,the walls of said cylindrical casing being formed with one or moreunsymmetrically placed outlet passages in communication with saidshallow chambers and leading from the vicinity of the point at whicharcing commences so as to provide vents through which products formed bythe arc escape from the switch chamber due to the pressure generatedtherein by the arc, said one or more outlet passages at any one portionalong the length of the cylindrical casing all being in the same side ofthe casing, said bafiie plates being formed with apertures through whichone of said electrodes moves, and some of said apertures being extendedfrom said electrode, but not extending entirely through said outletpassages to the outside of said cylindrical casing.

21. In a circuit interrupter, a tank, a body of arc extinguishing liquidtherein, means for establishing an arc in said liquid including amovable contact member, an arc extinguisher immersed in said liquid,said are extinguisher including a cylindrical casing having an openingin one end through which said contact member is moved to establish thearc, said casing having an opening through one side wall thereof and theother side walls and the other end thereof being closed to causepressure to be built up in the casing due to the gas formed by theaction of the are on said liquid, and means of insulating materialpositioned within said casing and having a passage for directing aportion of the fluid in said casing to flow laterally through the arcand out said opening through the side wall of the casing and into themain body of liquid in said tank.

22. In a circuit interrupter, a tank, a body of arc extinguishing liquidtherein, means for establishing an arc in said liquid including amovable contact member, an arc extinguisher immersed in said liquid,said are extinguisher in eluding a cylindrical casing having an openingin one end through which said contact member is moved to establish thearc, said casing having an opening through one side wall thereof and theother side walls and the other end thereof being closed to causepressure to be built up in the casing due to the gas formed by theaction of the arc on said liquid, and means of insulating materialpositioned within said casing and having a passage for directing aportion of the fluid in said casing to flow laterally through the arcand out said opening through the side wall of the casing and into themain body of liquid in said tank, and said passage in the means ofinsulating material and said opening through the side wall of the casingpermitting said flow of fluid to start before the moving contact hascleared the end of the opening through which it I is moved.

23. In a circuit interrupter, a tank, a body of arc extinguishing liquidtherein, means for establishing an arc in said liquid including amovable contact member, an arc extinguisher immersed in said liquid,said arc extinguisher including a cylindrical casing having an openingin one end through which said contact member is moved to establish thearc, said casing having an opening through one side wall thereof, andthe other side walls and the other end thereof being closed to causepressure to be built up in the casing due to the gas formed by theaction of the are on said liquid, and means of insulating materialpositioned within said casing, said means of insulating material beingprovided of the casing to establish the arc, and said passage having aportion extending laterally within the casing from said opening throughthe side wall thereof across the path of movement of said movablecontact member to permit fluid to flow laterally in the casing throughthe arc and out said opening through the side wall due to the pressurebuilt up in the casing.

24. In a circuit interrupter, a container having a body of liquidtherein, means for establishing an arc in said liquid including amovable contact member, an extinguisher for the arc ineluding a metalcasing in which the arc is established by said movable contact member,said metal casing having its exterior side walls covered with insulatingmaterial, and said metal casing having an opening through the side wallthereof and said covering of insulating material,

means of insulating material positioned inside of said metal casing,said means of insulating material having a passage extending laterallyacross the arc path within the metal casing and directing the fluid inthe metal casing to flow laterally through the arc and directly out saidopening through the side wall of the metal casing due to the gaspressure built up in the metal casing due to the action of the are onsaid liquid in the metal casing.

25. In a circuit interrupter, a container having a body of liquidtherein, means for establishing an arc insaid liquid including a movablecontact member, ,an extinguisher for the arc including a metal casing inwhich the arc is established by said movable contact member, said metalcasing having an opening therein through which said movable contact isactuated to establish the are, means of insulating material having apassage through which fluid flows through the arc and out said openingin the metal casing, said means of insulating material being formed of astack of plates of insulating material, and

said passage being defined on two opposite sides casing beingsubstantially closed except for an opening through which the movablecontact member is actuated whereby pressure is built up in said casingdue to the gas formed from said liquid by the arc, and said casinghaving a stack of contiguous plates of fibrous insulating material, saidstack of plates having a passage through which the movable contact isactuated in drawing the arc and through which the fluid in the casingflows to escape out said opening in the casing due to the pressuretherein.

27. In a circuit interrupter, a tank having a body of liquid therein,means for establishing an arc in said liquid including a movable contactmember, means for extinguishing the arc including a metal casingimmersed in said liquid, said casing being substantially closed exceptfor an opening through which the movable contact member is actuatedwhereby pressure is built up in said casing due to the gas formed fromsaid liquid by the arc, and said casing having a stack of contiguousplates of fibrous insulating material, said stack of plates having apassage through which the movable contact is actuated in drawing the arcand through which the fluid in the easing flows to escape out saidopening in the casing due to the pressure therein, and said passage being defined on two opposite sides by edges of said plates, and saidedges having portions extending substantially to the path of movement orsaid contact member.

28. In a circuit interrupter, a tank having a body of liquid therein,means for establishing an arc in said liquid including amovable contactmember, means for extinguishing the arc including a metal casingimmersed in said liquid, said. casing being substantially closed exceptfor an opening through which the movable contact member is actuatedwhereby pressure is buiit up in said casing clue to the gas formed fromsaid liquid by the arc, and said casing having a stack of contiguousplates of fibrous insulating material, said stack of plates having apassage through which the movable contact is actuated in drawing the arcand through which the fluid in, the casing flows to escape out saidopening in the casing due to the pressure therein, and said passagebeing defined on two opposite sides by edges of said plates, and saidedges having p01? tions extending substantially to the path of move.nent oi said contact member, and the pamage defined by said edges ofthe plates having a piurality oi recesses therealong at spacedintervals.

29. In a circuit interrupter, a body 0! liquid, an arc extinguishingstructure immersed in said body of liquid, means for causing an arc insaid are extinguishing structure whereby pressure is built up in saidare extinguishing structure due to the gas formed by the action of theare on said liquid, an enclosing casing surrounding said areextinguishing structure, said enclosing casing including a member ofmagnetic material which is generally cylindrical and of suchconfiguration as to move the arc in the arc extinguishing structure dueto the reaction between the arc current and the magnetic material of theenclosing casing, and said member of magnetic material strengtheningsaid enclosing casing to resist the pressure caused therein by the are.

30. In a circuit interrupter, a body of liquid, an arc extinguishingstructure immersed in said liquid and including a cylindricaliy shapedenclosing casing of magnetic material having a slot in one sideextending longitudinally thereof, said enciosing casing of magneticmaterial distorting the magnetic field due to the arc current to movethe are, and forming a pressure chamber about the are.

BENJAMIN P. BAKER. WINTHROP M. LEEDS.

